1. MICROSECOND TIME KEEPING TO IMPROVE POWER SYSTEM CONTROL & OPERATION
NARULA INSTITUTE OF TECHNOLOGY
Kolkata –

2. INTEGRATED ENERGY CONTROL CENTERS FOR POWERGRID MANAGEMENT
To Manage Power Networks spread over thousands of square miles
Require Time tagged MW, MVAR, Voltage and Frequency data from each substation
Require Time tagged Circuit Breaker and Protection Relay status data
Require Data from Disturbance Recorders and Sequential Event Recorders of each feeder
Require Time tagged Data from Power Management Units (PMU)for Voltage Angle at each Bus.
Monitor Fault Locator Data

4. IMPORTANCE OF VOLTAGE ANGLE
In an Alternating Current system, Power flows according to phase angle and not magnitude of voltage
For a generator or line outage, we have to respond within 200 ms or 10 cycles with higher generation for a 50 Hz system. In order to take this action, we must identify any overload on a generator or a line positively within 4 cycles (80 ms)
It is not possible to detect changes in MW values within 4 cycles using meters or transducers
It is possible to sample voltage waveforms at an interval of 4 cycles (80 ms) using PMU
Require Time tagged Data from Power Management Units (PMU)for Voltage Angle at each Bus.

6. IMPORTANCE OF VOLTAGE ANGLE (contd..)
Total Vector Error (TVE) for any measurement in percentage is
100 *√ [{Xr (n) – Xr }2 + {Xi (n) – Xi }2 ] / (Xr2 + Xi2 )
1% TVE for phase angle results in 20% error in calculation of Power flow
|V1 ||V2 |Sinδ / X
1% TVE for phase angle (IEEE standard till date) can be shown to be equivalent to 0.57 degrees
We need time accuracy among all PMU measurements within
(0.57*20 / 360) ms = 31.6 microseconds
To reduce the error in calculation of Power flow to 2%, we need a Time accuracy of 3.16 microseconds.(δ = 0.057)

7. IMPORTANCE OF FAULT LOCATOR DATA
IMPEDANCE TECHNIQUE
Fault Distance is calculated by transmitting a DC voltage signal and measuring the current to estimate the impedance of the fault segment. Since impedance per unit length is known, the distance can be calculated.
There is a TVE error of 1 to 2% in the estimated impedance per unit length
Transmission Voltage Distance between substations Accuracy in KM
132 KV KM km
220 KV KM km
400 KV KM km

8. IMPORTANCE OF FAULT LOCATOR DATA
TIME DOMAIN TECHNIQUE
Time domain techniques analyze the time taken for Fault-induced travelling waves to arrive at each end of the transmission line
The typical tower spacing on a high voltage transmission line is 300 meters.
So, the desired accuracy in terms of length is 300 m.
Fault-induced waves travel at the speed of light, 300 m/µs.
By time-tagging the arrival of fault-induced pulses at each end of the transmission line to within one microsecond, the fault can be located to within 300 m.
This accuracy is not dependent on environmental parameters as applicable for the impedance technique.

9. GLOBAL POSITIONING SYSTEM (GPS)
Provides better than microsecond accuracy with a 1 pps pulse of 100 nanoseconds width. The GPS is a worldwide satellite based radio navigation system operated and maintained by US Air Force
The GPS has a constellation of 24 earth satellites and ground stations. It provides two services :
Standard Positioning Service (SPS)
Precise Positioning Service (PPS)
The PPS is for use by US military and the SPS is available for all users around the world round the clock. Its timing accuracy is 340 nanoseconds. The SPS service is broadcast at MHz.
The GPS receiver extracts two pieces of information which are encoded into the satellite signals :
1. One pps strobe pulse of 100 nanosecond width.
2. The second is a serial message in a date and time format (ddmmyy;hhmm) for the 1 pps pulse referenced to Universal Coordinated Time (UTC).

10. GLONASS (Global Navigational Satellite System)
A system of 24 satellites is maintained by the Russian Federation (14 states) and may also be used
It is capable of nanosecond timekeeping with respect to Universal Coordinated Time maintained in Paris (UTC-BIPM)
GLONASS (Global Navigational Satellite System)

11. Use of INSAT Time & Frequency Broadcast System
INSAT is an Indian satellite system to provide Telecommunications, TV Broadcasting, Meteorological, Radio Networking, Natural Disaster Warning and Standard Time & Frequency System.
One of the satellites in the INSAT group is parked on the equator at 740 E. The Standard Time and Frequency Signal (STFS) service is given by National Physical Laboratory of India (NPLI) through one of the injected carrier narrowband channels (RN 5) of the Transponder 2 of the C/S band (6/2.5 GHz) of this Satellite.
The Channel has a RF bandwidth of 160 KHz and the modulation is FM with a baseband audio bandwidth of 10 KHz. The Uplink frequency of the injected carrier is MHz and the Downlink frequency is MHz. .
The Service was first made available through INSAT-1B with an accuracy of + 20 microseconds in March 1988.
After the replacement of INSAT-1B by INSAT-1D and subsequent satellites, a Differential STFS service is available since September, Correction of the propagation delay by using the latest satellite coordinates and differential correction has resulted in improvement of the accuracy of STFS time transfer between 125 nanoseconds to 1 microsecond anywhere within India.